(h)when the disposal of septic tank effluent is to a dispersion trench, the dispersion trench shall be 50 to 100 centimetres deep and 30 to 100 centimetres wide excavated to a slight gradient and shall be provided with 10 to 25 centimetres of washed gravel or crushed stones. Open jointed pipes placed inside the trench shall be made of unglazed earthenware clay or concrete and shall have minimum internal diameter of 75 to 100 millimeters. Each dispersion trench should not be longer than 30 metres and trenches should not be placed closer than 1.8 metres.
